The striatum, a region of the forebrain, was on average 10% larger in psychopathic individuals compared to a control group of individuals that had low or no psychopathic traits, in a new study1. Previous studies have pointed to an overly active striatum in psychopaths but have not conclusively determined the impact of its size on behaviors.

Our study’s results help advance our knowledge about what underlies antisocial behavior such as psychopathy. We find that in addition to social environmental influences, it is important to consider that there can be differences in biology, in this case, the size of brain structures, between antisocial and non-antisocial individuals,

said co-author Assistant Professor Olivia Choy. The understanding of the role of biology in antisocial and criminal behavior may help improve existing theories of behavior, as well as inform policy and treatment options.

Need For Thrills

Neuroscientists from Nanyang Technological University, Singapore (NTU Singapore), University of Pennsylvania, and California State University scanned the brains of 120 participants in the United States and interviewed them using the Psychopathy Checklist—Revised2, a psychological assessment tool to determine the presence of psychopathic traits in individuals.

Psychopathic traits include a lack of remorse for personal actions, a lack of empathy for others, and often criminal tendencies.

Through analyses of the MRI scans and results from the interviews to screen for psychopathy, the researchers linked having a larger striatum to an increased need for stimulation, through thrills and excitement, and a higher likelihood of impulsive behaviors.

The striatum is part of the basal ganglia, which is made up of clusters of neurons deep in the center of the brain. The basal ganglia receive signals from the cerebral cortex, which controls cognition, social behavior, and discerning which sensory information warrants attention.

In the past two decades, however, the understanding of the striatum has expanded, yielding hints that the region is linked to difficulties in social behavior. Previous studies have not addressed whether striatal enlargement is observed in adult females with psychopathic traits.

Nature Vs. Nurture

The neuroscientists say that within their study of 120 individuals, they examined 12 females and observed, for the first time, that psychopathy was linked to an enlarged striatum in females, just as in males. In human development, the striatum typically becomes smaller as a child matures, suggesting that psychopathy could be related to differences in how the brain develops.

A better understanding of the striatum’s development is still needed. Many factors are likely involved in why one individual is more likely to have psychopathic traits than another individual. Psychopathy can be linked to a structural abnormality in the brain that may be developmental in nature. At the same time, it is important to acknowledge that the environment can also have effects on the structure of the striatum,

said Choy.

Although not all individuals with psychopathic traits end up breaking the law, and not all criminals meet the criteria for psychopathy, there is a marked correlation. There is clear evidence that psychopathy is linked to more violent behavior.

The use of the Psychopathy Checklist—Revised in a community sample remains a novel scientific approach: Helping us understand psychopathic traits in individuals who are not in jails and prisons, but rather in those who walk among us each day,

Professor Robert Schug from the School of Criminology, Criminal Justice, and Emergency Management at California State University, Long Beach, who co-authored the study, said.

  1. Olivia Choy et al Larger striatal volume is associated with increased adult psychopathy, Journal of Psychiatric Research Volume 149, May 2022, Pages 185-193 ↩︎

  2. Hare, Robert D., Harpur, Timothy, J., Hakstian, A.R., Forth, Adelle E., and Hart, Stephen D. (1990) The Revised Psychopathy Checklist: Reliability and Factor Structure. Psychological Assessment, 2(3), 338-341 ↩︎

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